ABSTRACT
When chemists began preparing a large number of host compounds that could form supramolecular complexes, one of the most obvious and earliest applications was the use of such systems for analytical purposes.1 Receptor compounds that react selectively have been prepared for practically all possible analytes as described in thousands of publications.2 Also synthetic receptors for biogenic analytes, in contrast to natural biosensors, can always be equipped with suitable signaling elements; furthermore, they are usually more stable and can be adopted to any desired medium. As stated recently, natural biosensors comprising biomaterials have, with
Introduction and Some Principles ............................................................................ 49 Sensitivity and Selectivity ...................................................................................50 Compartmentalization for Higher Sensitivity ..................................................... 51 Signal Ampliˆcation with Molecular Wires ....................................................... 51 Reporter Groups for UV/vis and Fluorescence Measurement ............................ 51 Indicator Displacement Assay ............................................................................. 52 Sensor Array Systems and Combinatorial Searches ........................................... 52 Molecular Imprinting .......................................................................................... 52 Thin-Film Techniques/Thin-Film and Field-Effect Transistors .......................... 53 Covalent Bonding for Recognition ..................................................................... 53
Selected Analytes ..................................................................................................... 53 Environmental and Process Control .................................................................... 53 Drugs, Metabolites, Neurotransmitters/Chiral Discrimination ........................... 55 Amino Acids and Peptides ..................................................................................60 Detection of Natural Amino Acids without Protection .......................................60 Complexations of Protected Amino Acids and Peptides ..................................... 63 Nucleotides and Nucleosides ..............................................................................65 Carbohydrates .....................................................................................................68 Boronic Ester Reactions for Carbohydrate Analysis .......................................... 71 Biopolymers ........................................................................................................ 73
Outlook .................................................................................................................... 74 References ................................................................................................................ 74
the exception of the glucose monitor, almost entirely failed to achieve their potential as reagentless, real-time analytical devices.3 In this chapter, we can only discuss a few important principles ruling the choice of a practically useful synthetic host system and highlight applications with selected examples-if possible from recent papers in which one may ˆnd leading references. The chosen examples are usually promising for analysis in technical, environmental, biological, and medicinal ˆelds. The preferred examples are those suited for detection by optical or electrochemical methods and for analyses in aqueous media or in the gaseous state, with ¸uorescence offering a particular advantage with respect to sensitivity.4 The importance of host-guest complexes in water and the development of suitable receptor compounds have been aptly reviewed.5 Several techniques rely on the immobilization of supramolecular receptor compounds on surfaces and allow fast screening of many analytes, for example, in high-throughput screening (HTS). Besides optical detection, these physical methods comprise mass-sensitive detection (quartz crystal microbalance, QCM); electrochemical techniques (see Chapters 4 and 5) such as ion-sensitive electrodes (ISEs), which are not restricted to ions; photonic crystals (PCs); surface plasmon resonance (SPR); and others. First, we will discuss some methodological aspects, which then will be illustrated by examples from different analyte classes.
